This study will enroll 400 men and women in the Kampala district of Uganda, who are receiving or have recently initiated HAART. At baseline and monthly thereafter, research physicians and nurses at study clinics will assess each participant's clinical status and undertake study procedures. Each participant will be followed for 18 months, or until his/her death or loss to follow-up. Home visits will be conducted if participants miss their scheduled clinic appointments. We will perform nutritional assessments (anthropometry and dietary intake) at enrollment and several follow-up points, and laboratory measurements (CD4 cell counts and complete blood counts) every six months.